Injector for use in a device for combustion of corrosive products

ABSTRACT

The invention concerns an injector for the use in particular for combustion of corrosive products or a mixture thereof. Said injector comprises a flush cut tube housing, closed at one end, wherein are juxtaposed at least two flush cut tubes, and not more than eight tubes, said tubes perpendicularly passing through the wall, and at least one lateral branch pipe. The invention also concerns the use of said injector for implementing a method for the combustion of chlorine-containing corrosive products or a mixture thereof.

[0001] The subject of the present invention is an injector that can beused in particular in a device for the combustion of corrosive residuessuch as those containing halogenated, particularly chlorinated,hydrocarbons.

[0002] The industrial manufacture of chlorinated organic compoundsgenerates abundant quantities of residue, often containing chlorine.These residues may either be in the gaseous state, as for example in thecase of the manufacture of vinyl chloride or of its polymers orcopolymers, or in the state of liquid and/or tarry solid, obtained inthe manufacture of aliphatic, cycloaliphatic and/or aromatic chlorinatedhydrocarbons. The composition of these chlorinated residues variesaccording to their origin. Certain residues comprise chlorinated tarryproducts, at least some of the constituents of which contain more than 7carbon atoms per molecule. Other chlorinated residues comprisechlorinated C₄ compounds and/or chlorinated C₆ compounds. Thesechlorinated residues may be accompanied by other compounds comprisingchlorinated C₁ to C₄ constituents. These chlorinated residues may alsocomprise polychlorinated biphenyls (PCBs) used as dielectric fluids andcoolants and which need to be got rid of, given the ban on the use ofsuch products.

[0003] One means of solving the problem of the build-up of theseresidues and of the contamination of the air and/or of the water coursesinto which they may be discharged, is to burn them at high temperaturein a combustion chamber, with the recovery of gaseous hydrochloric acidwhich can be put into the form of an aqueous solution, and possibly theproduction of steam.

[0004] More specifically, these chlorinated gaseous and/or liquidresidues are burned in the presence of excess air and water attemperatures ranging from 900° C. to 1450° C., and generally between1200° C. and 1300° C. in an installation comprising, in particular, aburner into which the chlorinated residues and an oxidizer are injected;said burner being surmounted by a furnace in which the mean residencetime of the molecules is at least 3 seconds.

[0005] The hot gases leaving the furnace are quenched (rapidly cooled).The HCl formed is absorbed in absorbers, which leads to concentrated(33%) commercial solutions. Any chlorine that might be formed isabsorbed in an alkaline aqueous solution.

[0006] The burning of these residues is accompanied by lively combustionwhich can be obtained stably and continuously only in specially designedapparatus. The problem is that the combustion of this type of residue isaccompanied by difficulties and problems of various natures: theclogging of the burners and of the injectors particularly when theresidues are viscous, difficulties in finding the right settings forobtaining total combustion yielding hydrochloric acid containing only aminimum of free chlorine, together with zero production of carbon,corrosion, swift degradation of the parts of a burner if certain membersor walls of the apparatus are not protected with a refractory and/orantiacid coating, or with special arrangements, for example for theinjection of a significant volume of cold non-combustible gas around theflame.

[0007] Patent application FR 2509016, incorporated by reference intothis application, describes a device that can be used in particular forthe combustion of halogenated corrosive products or product mixtures orones likely to generate corrosive products, by bringing said products inthe dispersed state into contact with an oxidizing fluid at a highenough temperature to allow the cloud of particles formed to becomeincandescent.

[0008] This device, depicted in FIG. 1, comprises a combustion chamber(7), a head (1) for dispersing the phase that is to be burned into saidchamber, a connecting plate (2) connecting said dispersion head to thecombustion chamber, fluid inlets (3), (4) and (5), and a deflector (6).Also shown in this FIG. 1 is the pipe (30) for the outlet of thecombustion gases, and a blow-out seal (29).

[0009] The dispersion head (1) is an essential part of this device. Thisdispersion head (FIG. 3) comprises:

[0010] a device for the axial arrival of the phase that is to be burnedand of the auxiliary fluids, or injector (8), fitted with a guide (9),.

[0011] a chamber known as a swirl chamber for introducing swirl into aprimary fraction of the oxidizing phase (or of the oxidizer), allowingsaid primary fraction to be introduced into the combustion chamber inthe form of a vortex sink flow, to which enough momentum is imparted to,by transferring the momentum, disperse the phase that is to be burned,said swirl chamber comprising a tangential inlet (15) leading saidprimary fraction of the oxidizing phase into an annular space containedbetween an external wrapper (16) and an internal wrapper (17) perforatedat its upstream part and behaving like a multitude of tangential inlets,said swirl chamber ending in a conical part (18), the end of thisconical part (18) and the injector (8) are dimensioned and arranged insuch a way as to form a narrow annular passage (references 26 and 27);

[0012] an inlet into the combustion chamber of a secondary fraction ofthe oxidizing phase (21);

[0013] a deflector (24) toward the base of the combustion zone, allowingsaid secondary fraction to be deflected down toward the base of thecombustion zone, said deflector delimiting a passage (28) around thecombustion zone, the inlet (21) and the deflector (24) being dimensionedand arranged in such a way as to allow the secondary oxidizing fractionsto constitute the complement of the oxidizing phase needed forcombustion and at the same time to stabilize the incandescent cloud andto cool the deflector and the connecting plate (19), which bears thedeflector (24), the shell rings (20), the inlet orifices (21) and thefixing means (22), which can be adjusted during operation with respectto the sole (25) of the combustion chamber;

[0014] an annular leakage space (23) formed between the sole (25) andthe plate (19), which allows a second part of the secondary fraction ofthe oxidizing phase to be introduced.

[0015] The dimensioning recommended in this document, of the variousparts concerned is such that the ratio of the outside diameter (27) tothe inside diameter (26) of the narrow annular passage is between 1.1and 1.6 and preferably between 1.15 and 1.4 and that the ratio of thediameter (28) of the passage left by the deflector to the diameter (27)mentioned hereinabove is between 1.5 and 5 and preferably between 2 and4.5.

[0016]FIG. 2 depicts details of the device for the axial arrival of thephase that is to be burned and of the auxiliary fluids, or injector.

[0017] This injector comprises:

[0018] a guide (9),

[0019] a tube (12) for bringing in the fluid containing the productsthat are to be burned,

[0020] auxiliary coaxial inlets, namely concentric tubes (10), (11) and(12) which, via the annular spaces (13) and (14) allow the top-up fuelsand/or oxidizers to be introduced. Altering the geometry of the tube(10) makes it possible also to alter the configuration of the combustioncloud and to fulfill an adjustment function.

[0021] Such a device is well suited to the burning of chlorinatedresidues. The applicant company has used a similar device for burningliquid chlorinated residues.

[0022] Thus, for example, the applicant company has used this device forthe combustion of residues containing approximately 77% by weight ofchlorine. These residues in particular comprise hexachorobutadiene,hexachlorobenzene, tetrachlorobenzene, pentachlorobenzene andhexachloroethane.

[0023] This residue is a viscous liquid, the crystallization point ofwhich is higher than 160° C.

[0024] The complete installation comprises a burner/combustion chamberassembly as depicted in FIGS. 1, 2 and 4. In FIG. 4, which depicts thedispersion head, the shell rings (20) have been omitted and said swirlchamber ends in a frustoconical part (18), the end of this part and theinjector (8), the guide (9) of which is shorter, are arranged in such away as to form a narrow annular passage (references 26 and 27). In thisdevice, the ratio (27)/(26) is 1.28 and the ratio (28)/(27) is 4. Theinstallation also comprises:

[0025] a quenching device (not depicted in the figures),

[0026] a string of 4 Venturi-type absorbers (not depicted in thefigures),

[0027] and a neutralizing column (not depicted in the figures).

[0028] The depression is created in the combustion chamber by virtue of4 Venturis in series and an extractor.

[0029] The residue, the flow rate of which is 2500 kg/h, is conveyed tothe burner by the concentric tube (12). The temperature in thecombustion chamber is 1200° C. The depression in this chamber is kept atapproximately 100 mbar.

[0030] 2700 Sm³/h of atomization air at 0.5×10⁵ Pa is introduced throughthe annular space (27)/(26), that is to say via the tangential inlet(15).

[0031] 10 Sm³/h of tertiary air is injected via the annular space (14)between the tubes (10) and (11).

[0032] An overall secondary-air flow rate of 2500 Sm³/h is made up of afirst flow of secondary air drawn in through the holes (21) in thebottom plate (19) and of a second flow of secondary air drawn in throughthe annular leakage space (23).

[0033] The composition of the flue gases leaving the combustion chamberis as follows (percentages by weight): O₂  3.7% N₂ 57.0% CO₂ 20.3% Cl₂ 0.4% HCl 14.5% H₂O  4.1%

[0034] After these flue gases have been treated in the absorbers, aclear hydrochloric solution is obtained containing 30 wt % HCl.

[0035] The Applicant company has found that, although it yieldedexcellent combustion of said chlorinated residues, this device did, overtime, exhibit disadvantages due in particular to the device for theaxial arrival of the chlorinated residues to be burned and of theauxiliary fluids or injector depicted in FIG. 2.

[0036] What the Applicant company actually found was that the passagesin the rings formed by the concentric tubes often became blocked. Theseblockages led to said injector being changed on average every 30 days.

[0037] Because of the expensive material (tantalum) of which theseconcentric tubes are made, these operations had a serious impact on thebudget. These changes took several hours, and also led to costly coolingof the furnace, giving rise to a drop in productivity.

[0038] In addition, as the tubes were becoming blocked, the combustionof the chlorinated derivatives was disturbed by a haphazard supply offluids (fuel and oxidizer), leading to a disruption in the quality ofthe outfall.

[0039] In order to reduce the cost of the operations, the Applicantcompany modified the nature of the material of which the tubes were madeand used ordinary steel.

[0040] In addition to the blockages mentioned above, the Applicantcompany found that the tubes became holed, leading to migration offluids from one tube to the other.

[0041] Another disadvantage observed by the Applicant company waserosion of the “tip” or end of the injector, leading to poor atomizationof the products to be burned and therefore to poor combustion.

[0042] The Applicant company has now found that it is possible toreduce, or even to eliminate, the abovementioned drawbacks by modifyingthe design of said injector.

[0043] The subject of the present invention is therefore an injector Inas depicted schematically in FIG. 5, that can be used in particular in adevice for the combustion of corrosive products or product mixtures orthose likely to generate corrosive products by bringing said products(in the dispersed state) into contact with an oxidizer at a temperaturethat allows said products to burn, characterized in that it comprises astraight cylindrical wrapper tube (E), closed at one end by a wall (P),inside which tube are juxtaposed at least 2 straight tubes (T) and atmost 8 tubes, preferably 4 or 5 tubes, said tubes passing at rightangles through the wall (P), and at least one lateral nozzle (TL)situated near the wall (P).

[0044] According to the present invention, these tubes (T) may haveidentical or different inside diameters. These tubes (T) may be arrangedrandomly but it is preferable for them to be arranged in a ring. FIG. 6depicts a section through the injector on AA′ of FIG. 5, said injectorcontaining 4 tubes of the same diameter arranged in a ring. FIG. 6depicts a section through an injector comprising 5 tubes: 4 tubes of thesame diameter are arranged in a ring, and the 5th, of smaller diameter,is central.

[0045] According to the present invention, at least one of the tubes (T)conveys corrosive products or product mixtures for burning and at leastone of the tubes (T) conveys all or some of the oxidizer needed for thecombustion. This oxidizer may be air, oxygen-enriched air or,alternatively, oxygen.

[0046] Depending on the calorific value of the products that are to beburned, a top-up fuel such as propane, vent gases from the manufactureof PVC, fuel, etc. may be supplied. This top-up fuel, according to thepresent invention, may be conveyed by one of the tubes (T) of thedevice.

[0047] The space created by the juxtaposed tubes (T) inside the wrappertube (E)—which space is denoted by (ET)—may be swept by a fluid forcooling the tubes (T) or alternatively may bring in top-up oxidizer forcombustion.

[0048] This fluid is preferably air, humidified air, water, steam and isintroduced, preferably tangentially, to the wrapper tube (E) andpreferably at its lower part via a nozzle (TL).

[0049] The thicknesses of the tubes (T) and of the tube (E) may vary toa large extent. They are dependent on the material used and on thecorrosiveness of the products that are to be destroyed. Advantageously,these thicknesses will be at least equal to 1.5 mm and preferablybetween 1.5 and 3 mm.

[0050] According to one embodiment of the injector In according to theinvention, it is recommended that the various tubes (T) be dimensionedin such a way that the ratio of the outside diameter De of a tube (T) tothe inside diameter Di of the same tube (T) is between 1.2 and 1.6 andpreferably between 1.25 and 1.5.

[0051] Furthermore, according to the present invention, the ratio of thetotal internal surface area of the tubes (T), ΣS_(T), to the internalpassage cross-sectional area of the tube (E), S_(ET), containing n tubes(T) is between 1 and 1.50 and preferably between 1.05 and 1.25.

[0052] The length of the tube (E) is 20 to 30 times the inside diameterof said tube (E), and preferably 22 to 26 times this diameter.

[0053] It is the task of the person skilled in the art to select theprecise ratios, within the limits recommended above, according inparticular to the flow rates chosen for the corrosive products that areto be destroyed and the various other fluids.

[0054] The tubes are supplied upstream of the wall (P) by hoses whichare fitted with “quick-fit” connectors (J) of the Surlock® type,allowing them to be fitted and removed quickly.

[0055] Upstream of the wall (P), the tubes (T) may adopt a curvature soas to make them easier to connect to the supply hoses. Their lengths,still upstream of the wall (P) may be identical or different and dependon the size of the device.

[0056] The ends of the tubes (T) are at the same level (in the sameplane) as the end of the tube (E) (line BB′ in FIG. 5).

[0057] According to the present invention, the injector In of thepresent invention can be arranged vertically or horizontally.

[0058] Another subject of the present invention also relates to the useof said injector described hereinabove for implementing a method for thecombustion of corrosive products or corrosive product mixtures likely togenerate corrosive products.

[0059] According to this method, the phase(s) containing the products tobe burned is (are) introduced in liquid and/or gaseous form along theaxis of the vortex sink formed by the primary fraction of the oxidizingphase practically as far as the depression region of said vortex sink,the momentum conferred upon the vortex sink being enough to cause thephase to be burned to be dispersed into particles through the transferof momentum and the secondary fraction of the oxidizing phase isintroduced separately at a flow rate and in one or more directionsmaking it possible, simultaneously, to provide the complement ofoxidizing phase needed for combustion, to cool the part of the devicesurrounding the combustion zone and, in particular, the deflectorallowing the secondary fraction to be deflected toward the base of thecombustion zone and to stabilize the incandescent cloud.

[0060] The products to be burned are introduced preferably in liquidform at a flow rate ranging from 500 to 3500 kg/h and preferably between1200 and 3000 kg/h. When introduced in gaseous form, their flow rate isbetween 5 and 15 Sm³/h.

[0061] The flow rate of the primary fraction of the oxidizing phase(also known as the atomization air) is between 500 and 5000 Sm³/h andpreferably between 2000 and 3500 Sm³/h.

[0062] In the implementation of the method according to the invention,the combustion zone is at a depression of the order of 10 to 1500 Pabelow atmospheric pressure. The pressure of the primary fraction of theoxidizing phase is 0.1 to 8.5×10⁵ Pa higher and preferably 0.2 to0.6×10⁵ Pa higher than the pressure in the combustion zone.

[0063] The secondary fraction of the oxidizing phase may be introducedinto the combustion chamber by induction at various points given thedepression in the combustion chamber.

[0064] This secondary fraction may be introduced in a single flow,particularly deflected toward the combustion zone by means of adeflector as mentioned hereinabove, or in the form of two flows flowingone on each side of said reflector.

[0065] The total flow rate of the secondary fraction of the oxidizingphase can vary to a large extent. In general, this flow rate iscalculated in such a way that the ratio of the total flow rate of thesecondary fraction to the flow rate of the primary fraction is between0.1 and 10 and preferably between 0.9 and 5.

[0066] Given the nature of the products to be burned, it is possible tosupply a top-up fuel in liquid or gaseous form, and it is advantageousthat this fuel be introduced through one of the tubes of the injectoraccording to the invention.

[0067] According to the present invention, water may also be introducedinto the combustion zone. This introduction is also advantageouslyachieved through one of the tubes of the injector according to theinvention.

[0068] A top-up of oxidizing phase known as tertiary phase may be used.

[0069] If it is, this top-up is made coaxially using a nozzle arrangedat right angles to the wrapper tube of the injector. This top-up isintroduced at a pressure ranging from 2 bar to 10 bar and preferably ata pressure ranging from 4 to 6 bar.

[0070] The use of the injector of the present invention, aside fromyielding remarkable combustion of the corrosive products, equivalent tothat achieved by burners of the prior art, has the advantage that saidcorrosive products can be combusted over several months without therebeing any blockage and/or holing of one (or more) tube(s) of which saiddevice is made. In the event that a blockage occurs in one or moretubes, there are several simple and quick options:

[0071] the use of a simple flexible wand introduced into the tube mayallow the blockage to be removed without shutting the burner down (thefurnace is at a depression),

[0072] or alternatively, if the blockage is more sizeable, the entiredevice can be changed quickly, in under one hour, without an appreciablereduction in furnace temperature.

[0073] The injector of the present invention makes it possible tocombust corrosive products or product mixtures under remarkableconditions.

[0074] This injector applies quite particularly to the combustion ofchlorinated liquid residues which are generally viscous, possibly ladenwith solid particles in suspension.

[0075] These chlorinated residues as defined earlier often contain morethan 40%, or even more than 75% by weight of chlorine. However, it isclearly understood that the device of the present invention can be usedfor the combustion of corrosive products, or those likely to yieldcorrosive products, containing quantities of chlorine well below 40%.

[0076] The injector according to the invention also makes it possible toburn, at the same time as the liquid chlorinated residues, gaseouschlorinated residues such as, in particular, the vent gases originatingfrom the manufacture of polyvinyl chloride.

[0077] Another advantage is the possibility of quickly changing over thesupply to a tube, given the connections (J).

[0078] The tubes (T) can also be cooled by causing air, water orhumidified air to pass through the space (ET).

[0079] Given the fact that the injector of the present invention canoperate for several months without blockage, better stability in theoperation of the furnace, in the combustion, and improved safety areobserved. The vent gases are also found to have a constant quality.

[0080] The example which follows illustrates the invention.

[0081] Injector according to the invention as depicted in FIGS. 5 and 6.

[0082] Number of tubes (T):4:(T1), (T2), (T3), (T4).

[0083] The inside (Di) and outside (De) diameters of the 4 tubes areidentical.

[0084] inside diameter: 15 mm

[0085] outside diameter: 21 mm

[0086] De/Di=1.4

[0087] internal surface area of a tube: 177 mm²

[0088] external surface area of a tube: 346 mm²

[0089] total external surface area of the 4 tubes: 346.36×4=1385 mm²

[0090] length of tubes (T): 1.45 m (including the part upstream of thewall (P))

[0091] Wrapper tube (E):

[0092] inside diameter: 51 mm, namely an internal surface area of 2043mm²

[0093] cross-sectional area of the passage SET between the wrapper tube(E) and the tubes (T): 2043−1385=658 mm²

[0094] ratio: ΣS_(T)/S_(ET)=177×4/658=1.07

[0095] length of the tube (E)=1.20 m

[0096] The tubes T1, T2, T3 and T4 are arranged as indicated in FIG. 5.

[0097] This injector is designed for an installation for the combustionof residues as described previously in the description, that is to saythat the injector In of the present invention is arranged in place ofthe injector (8).in the dispersion head depicted in figure (4), andpenetrates said dispersion head over a length of 48 cm (CC′) measuredfrom the guide (9), namely 72 cm outside of said head (DD′)

[0098] The chlorinated residues to be destroyed consist on the one handof PCBs and, on the other hand, of chlorinated residues containingapproximately 80% by weight of chlorine and consist essentially ofhexachlorobutadiene, hexachlorobenzene, tetrachlorobenzene and aliphaticchlorinated products such as hexachloroethane.

[0099] The PCBs are introduced via the tube (T1) at a flow rate of 400kg/h.

[0100] The chlorinated residues are introduced by the tube (T2) at aflow rate of 1600 kg/h.

[0101] The gaseous chlorinated vent gases originating from thepreparation of PVC are introduced via the tube (T3) at a flow rate of 10m³/h. Water is introduced through the tube (T4) at a flow rate of 500kg/h.

[0102] Tertiary air is introduced into the wrapper (E) by means of thenozzle (TL) at a flow rate of 10 m³/h.

[0103] 2700 Sm³/h of primary (or atomization) air is introduced at apressure of about 0.5×10⁵ Pa into the annular space (27/26) via thetangential inlet (15).

[0104] An overall flow rate of secondary air of about 2500 Sm³/h is madeup of a first flow of secondary air drawn in through the holes (21) inthe bottom plate (19) and a second flow of secondary air drawn inthrough the annular leakage space (23).

[0105] The ratio (27)/(26)is 1.28 and the ratio (28)/(27)is 4.

[0106] Furthermore, the head of the injector In is 6.8 cm from the planeformed by the ends of the deflector (24).

[0107] The device for the combustion of these residues ran for 6 monthswithout any blockages being observed in the injector of the invention.By contrast, when operating with an injector of the prior art asdepicted schematically in FIG. 2, blockages are observed after 30 daysof operation.

[0108] The mean composition of the flue gases leaving the combustionchamber is as follows (percentages by weight): O₂  6.0% N₂ 58.0% CO₂15.7% Cl₂  0.4% HCl 15.8% H₂O  4.0%

[0109] After these flue gases are treated as mentioned previously in thedescription, there is obtained a clear solution containing about 30 wt %of HCl.

[0110] The flue gases discharged into the atmosphere contain no freechlorine.

[0111] Analyses performed on the flue gases show that the PCB content isbelow 0.5 μg/Sm³; the content of polychorodibenzofuran andpolychlorodibenzodioxin in the gases is 0.1 ng/m³.

1. An injector In that can be used in particular in a device for thecombustion of corrosive products or product mixtures, by bringing saidproducts (in the dispersed state) into contact with an oxidizer at atemperature that allows said products to burn, characterized in that itcomprises a straight cylindrical wrapper tube (E), closed at one end bya wall (P), inside which tube are juxtaposed at least two straight tubes(T) and at most eight straight tubes (T) of identical or differentinside diameters, passing at right angles through the wall (P), and atleast one lateral nozzle (TL), situated near the wall (P), and in thatat least one of the tubes (T) conveys corrosive products or productmixtures for burning and at least one of the tubes (T) conveys all orsome of the oxidizer needed for the combustion of said corrosiveproducts.
 2. The injector In as claimed in claim 1, characterized inthat it comprises 4 tubes (T).
 3. The injector In as claimed in claim 2,characterized in that the tubes are arranged in a ring.
 4. The injectorIn as claimed in one of claims 1 to 3, characterized in that the ratioof the outside diameter De of a tube (T) to the inside diameter Di ofthe same tube (T) is between 1.2 and 1.6 and preferably between 1.25 and1.5.
 5. The injector In as claimed in one of claims 1 to 5,characterized in that the ratio of the total internal surface area ofthe tubes (T), ΣS_(T), to the internal passage cross-sectional area ofthe wrapper tube (E), S_(ET,) containing n tubes (T) is between 1 and1.50 and preferably between 1.05 and 1.25.
 6. The injector In as claimedin any one of claims 1 to 5, characterized in that the length of thewrapper tube (E) is 20 to 30 times the inside diameter of said wrappertube (E).
 7. The injector In as claimed in any one of claims 1 to 6,characterized in that the end of the tubes (T) are at the same level asthe ends of the tube (E).
 8. The injector In as claimed in any one ofclaims 1 to 7, characterized in that the tubes are supplied upstream ofthe wall (P) by hoses fitted with “quick-fit” connectors.
 9. Theinjector In as claimed in any one of claims 1 to 8, characterized inthat the lateral nozzle (TL) conveys air.
 10. The use of an injector Inas claimed in any one of claims 1 to 9 in a method for the combustion ofcorrosive products or product mixtures or those likely to generatecorrosive products.
 11. The use of an injector In as claimed in claim10, characterized in that the corrosive products or product mixtures arechlorinated gaseous and/or liquid residues.